Alternative pollinator taxa are equally efficient but not as effective as the honeybee in a mass flowering crop

Abstract

Summary 1.The honeybee Apis mellifera is currently in decline worldwide because of the combined impacts of Colony Collapse Disorder and the Varroa destructor mite. In order to gain a balanced perspective of the importance of both wild and managed pollination services, it is essential to compare these services directly, a priori, within a cropping landscape. This process will determine the capacity of other flower visitors to act as honeybee replacements. 2. In a highly modified New Zealand agricultural landscape, we compared the pollination services provided by managed honeybees to unmanaged pollinator taxa (including flies) within a Brassica rapa var. chinensis mass flowering crop. 3. We evaluate overall pollinator effectiveness by separating the pollination service into two components: efficiency (i.e. per visit pollen deposition) and visit rate (i.e. pollinator abundance per available flower and the number of flower visits per minute). 4. We observed 31 species attending flowers of B. rapa. In addition to A. mellifera, seven insect species visited flowers frequently. These were three other bees (Lasioglossum sordidum, Bombus terrestris and Leioproctus sp.) and four flies (Dilophus nigrostigma, Melanostoma fasciatum, Melangyna novae-zelandiae and Eristalis tenax). 5. Two bee species, Bombus terrestris and Leioproctus sp. and one fly, Eristalis tenax were as efficient as the honeybee and as effective (in terms of rate of flower visitation). A higher honeybee abundance, however, resulted in it being the more effective pollinator overall. 6. Synthesis and applications. Alternative land management practices that increase the population sizes of unmanaged pollinator taxa to levels resulting in visitation frequencies as high as A. mellifera, have the potential to replace services provided by the honeybee. This will require a thorough investigation of each taxon's intrinsic biology and a change in land management practices to ensure year round refuge, feeding, nesting and other resource requirements of pollinator taxa are met.

Per-visit pollinator performance and regional importance of wild Bombus and Andrena (Melandrena) compared to the managed honey bee in New York apple orchards

“…Here, pollinator importance is the product of (1) visitation frequency of floral visitors and (2) pervisit efficiency (Rader et al 2009;Vázquez et al 2005). We used relative abundance as a proxy for visitation frequency, as justified by Gallai et al (2009).…”

“…Pollinator importance is the relative contribution of a floral visitor to the pollination of a plant population (here, an orchard), and incorporates two components of pollination service: pervisit performance and relative abundance (Olsen 1996;Rader et al 2009). Pollinator importance scales up per-visit performance by accounting for the fact that an abundant pollinator with a low pervisit impact on pollination may contribute as much, if not more, to overall pollination as a rare pollinator that has high per-visit impact.…”

On managing the red mason bee (Osmia bicornis) in apple orchards

“…Several native wild bee species have been identified to be capable of replacing or at least supplementing the decreasing number of honeybees (Kremen et al 2002;Rader et al 2009). In 2002, Bosch and Kemp (2002) published a review that described how to establish bee species as crop pollinators using three Osmia sp.…”

Relative abundance and movement of flower visitors within ‘Black Doris’ plum orchards in Hawke’s Bay, New Zealand

“…In New Zealand, calliphorid and syrphid flies are known to be effective pollinators of other crops (Rader et al 2009;Howlett 2012). Moreover, calliphorids will forage under cool, low light conditions that are not preferred by honey bees (Howlett et al 2013), and are active throughout all seasons of the year (Howlett et al 2016).…”

“…Although these experiments are time consuming, further trials replicating these methods will help to build sufficient sample sizes for individual species in subsequent years. Further work would also allow for species-level analysis to be conducted as has been achieved for other crops (Rader et al 2009;Howlett et al 2013).…”